Piston pump

ABSTRACT

The invention relates to a piston pump having a piston that is axially displaceable in a bush. In order to keep the piston in the bush in a manner secured against loss, a tubular filter is secured to the bush in the extension thereof; the filter has a smaller inside diameter than the bush and in this way keeps the piston in the bush.

BACKGROUND OF THE INVENTION

The invention relates to a piston pump as defined hereinafter.

The piston pump is intended in particular as a pump in a brake system ofa vehicle and is used to control the pressure in wheel brake cylinders.Depending on the type of brake system, the abbreviations ABS, ASR, FDRand EHB are used for such brake systems. In the brake system, the pumpserves for instance to return brake fluid from a wheel brake cylinder ora plurality of wheel brake cylinders to a master cylinder (ABS) and/orto pump brake fluid out of a supply container into a wheel brakecylinder or a plurality of wheel brake cylinders (ASR or FDR or EHB). Ina brake system with wheel slip control (ABS or ASR) and/or a brakesystem serving as a steering aid (FDR) and/or an electrohydraulic brakesystem (EHB), the pump is needed. With the wheel slip control (ABS orASR), locking of the wheels of the vehicle during a braking eventinvolving strong pressure on the brake pedal (ABS) and/or spinning ofthe driven wheels of the vehicle in the event of strong pressure on thegas pedal (ASR) can for instance be prevented. In a brake system servingas a steering aid (FDR), a brake pressure is built up in one or morewheel brake cylinders independently of an actuation of the brake pedalor gas pedal, for instance to prevent the vehicle from braking out ofthe lane desired by the driver. The pump can also be used in anelectrohydraulic brake system (EHB), in which the pump pumps the brakefluid into the wheel brake cylinder or wheel brake cylinders if anelectric brake pedal sensor detects an actuation of the brake pedal, orin which the pump is used to fill a reservoir of the brake system.

Many such piston pumps are known. One example that can be named is thepiston pump known from German Patent Disclosure DE 41 07 979 A1.

The known piston pump has a rodlike piston, which is displaceably guidedaxially in a bush. For driving the piston to execute a reciprocatingstroke motion, an eccentric element drivable to rotate by an electricmotor is used, which acts upon the piston on a face end protruding outof the bush. The bush is inserted into a cylinder bore of a pumphousing.

For assembling the known piston pump, its piston is introduced into thebush, and the bush is then screwed into the cylinder bore. The assemblyoften proves to be difficult, since the piston is not retained in thebush until after the bush has been inserted into the pump housing. Thismakes assembly more difficult, especially in the case of piston pumpsthat have a piston restoring spring that forces the piston out of thebush. A further hindrance to assembly in many such piston pumps, whichare intended as pumps in hydraulic vehicle brake systems, is that acheck valve is mounted as an inlet or outlet valve on the piston, sothat even more individual parts have to be put together that gain asecure hold only after the bush together with the piston is insertedinto the cylinder bore of the pump housing.

OBJECT AND SUMMARY OF THE INVENTION

The piston pump according to the invention has the advantage that thepiston pump can be premounted as a compact structural group outside thepump housing. This structural group is sturdy and easily manipulated,and all of its parts are held together in a manner secured against loss.The structural group can be inserted simply, at minimal expenditure oflabor, into a cylinder bore of the pump housing, for instance, bypress-fitting.

The piston pump has a hollow-cylindrical or tubular filter, which hasapproximately the same diameter as the bush and is mounted on the bushon the end that protrudes from the piston. The filter surrounds thebush, or a part of the piston protruding from the bush. The filter has aloss-prevention means, which protrudes inward with respect to a bore ofthe bush and keeps the piston in the bush, for instance on an annularshoulder or at a right mounted on the piston. The loss-prevention meansmay be embodied annularly or hollow-cylindrically, for instance; thatis, at least one point the filter has a smaller inside diameter than thebush. However, it is also sufficient for the loss-prevention means to beembodied as a protrusion or the like on only one or a few points of thecircumference. Depending on the embodiment, the loss-prevention meanscan in principle be located at any arbitrary point in the axialdirection of the filter in the axial direction.

Mounting the filter on the bush in the extension thereof can be done forinstance by adhesive bonding, screwing, a bayonet mount, and so forth.The mounting can also be done for instance by means of a press-fit, asnap or detent connection, or by a deformation such as crimping orcaulking.

With the aid of the easily mountable filter, a preassembled structuralgroup that includes the bush and the piston is obtained. This has theadvantage that the piston pump can easily be inserted into the pumphousing with only a few mounting steps or a few manual operations.

The filter can be embodied and mounted on the bush in such a way thateven before these parts are inserted into the pump housing, an axialalignment of the piston relative to the bush is created via this filter.

This advantageously makes the installation of the parts that have to bebuilt into the pump housing substantially easier.

The invention will be better understood and further objects andadvantages thereof will become more apparent from the ensuing detaileddescription of preferred embodiments taken in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial section through a piston pump according to theinvention;

FIGS. 2 and 3 show details indicated by reference numeral II in FIG. 1of modified embodiments of the piston pump of the invention, on adifferent scale; and

FIG. 4 shows a detail of a further modified embodiment of a piston pumpaccording to the invention, indicated by reference numeral IV in FIG. 1,on a different scale.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The piston pump of the invention, indicated overall by reference numeral10, shown in FIG. 1 has a bush 12, which is inserted into a steppedcylinder bore 14 of a hydraulic block that forms a pump housing 16. Thehydraulic block, of which only a fragment surrounding the piston pump 10is shown in the drawing, is part of a slip-controlled hydraulic vehiclebrake system not otherwise shown here. Inserted into it besides thepiston pump 10 are hydraulic components, such as magnet valves andhydraulic reservoirs, and a master cylinder and a wheel brake cylinderare connected to it. By means of the hydraulic block, the hydrauliccomponents are hydraulically connected to one another.

The bush 12 is a hollow-cylindrical turned part, with a bush bottom 18integral with it. Its cylindrical inside surface is rolled orcold-headed. The bush 12 may, however, also be produced in an especiallysimple way as a cold-headed part without metal-cutting surfacemachining.

A rodlike piston 20 is received over approximately half its length inthe bush 12. An end of the piston 20 located inside the bush 12 isaxially displaceably guided by a guide ring 26 on the inside surface ofthe bush 12 and is sealed off by a sealing ring 28. The other end of thepiston 20, which protrudes from the bush 12, is axially displaceablyguided by means of a guide ring 22 directly in the cylinder bore 14 ofthe pump housing 16 and is sealed off by a sealing ring 24 on the pumphousing 16.

For admitting fluid, the piston 20 is provided with an axial blind bore30 extending from its end located in the bush 12; near its bottom, thisbore is intersected by transverse bores 32. The piston 20 has a diametersmaller than an inside diameter of the bush 12, so that an annularinterstice 34 exists between the piston 20 and the bush 12. The blindbore 30 and the transverse bores 32 communicate through this interstice34 and an open face end of the bush 12, with an inlet bore 36 whichdischarges radially to the piston pump 12 into the cylinder bore 14 atthe level of the open face end of the bush 12.

As its inlet valve 38, the piston pump 10 of the invention has aspring-loaded check valve, which is mounted on the end of the piston 20located in the bush 12. An orifice of the blind bore 30 is embodied as aconical valve seat 40, against which a valve ball 42 is pressed, as avalve closing body, by a helical compression spring, acting as a valveclosing spring 44. The valve closing spring 44 is braced against abottom of a cup-shaped valve cage 46, which is produced as a deep-drawnpart from sheet metal and has axial and/or radial openings 48. On itsopen end, the valve cage 46 has an encompassing annular shoulder 50,with which it rests on the face end of the piston 20 located in the bush12, and a radial flange 52, at which it is pressed against the face endof the piston 20 by a piston restoring spring 54. The valve ball 42 andthe valve closing spring 44 are received in the valve cage 46. Thepiston restoring spring 54 is embodied as stronger than the valveclosing spring 44. The piston restoring spring 54 is braced against thebush bottom 18.

To drive the piston 20 to execute an axially reciprocating strokemotion, the piston pump 10 of the invention has an eccentric element 56,which can be driven to rotate by an electric motor and against whosecircumference the piston 20 is pressed by the piston restoring spring54.

The guide ring 26 located in the bush 12 and the sealing ring 29 arefixed on the piston 20 in the axial direction between the radial flange52 of the valve cage 46 and a support ring 58 that rests on an annularshoulder 60 of the piston 20.

In the region of the bush bottom 18, a cylindrical closure element 62 ispressed onto the bush 12; it acts to provide pressure-tight closure ofthe cylinder bore 14 and to fix the bush 12 in the pump housing 16. Theclosure element 62 may also be joined to the bush 12 via a crimpedconnection; a radial play may be provided between the bush 12 and theclosure element 62. An outlet valve 64 in the form of a spring-loadedcheck valve is accommodated in the closure element 62. The closureelement 62 has a coaxial blind bore 66, into which a helical compressionspring as a valve closing spring 68 and a valve ball 70 as a valveclosing body are inserted. The valve ball 70 cooperates with a conicalvalve seat 72 which is provided at an orifice of a center bore 74 thataxially penetrates the bush bottom 18. The valve seat 72 can be shapedand hardened by stamping, or it can be made in a single operation withthe bush 12 in the cold-heading thereof. A fluid outlet is providedthrough radial conduits 76 between the bush bottom 18 and the closureelement 62, into a radial outlet bore 78 in the pump housing 16.

In the extension of the bush 12, on its open end, a hollow-cylindricalfilter 80 is mounted, which has approximately the same diameter as thebush 12. The filter 80 has a filter screen 82, in the form of a tubularcloth, which is spray-coated with a filter scaffold of plastic. Thecloth is of metal or plastic. On its face end toward the bush 12, thefilter 80 has a ring 86a, and on its end toward the eccentric element 56the filter 80 has a ring 86b. The two rings 86a, 86b are integrallyjoined together by ribs 88. The ribs 88 and the rings 86a, 86b form thefilter scaffold. A tubular filter cloth 90 rests in the filter screen82. An inflow to the piston pump 10 is effected from the inlet bore 36,between the rings 86a, 86b and ribs 88 of the filter scaffold, throughthe filter screen 82 and the filter cloth 90 into the open end of thebush 12. To allow the fluid to flow out of the inlet bore 36 through thefilter cloth 90 of the filter 80 into the interstice 34, there is acircumferential gap between the ring 86a of the filter 80 and the piston20, or else the ring 86a is provided with some axial openings.

For mounting on the bush 12, the ring 86a of the filter 80 has anaxially protruding collar 92, which is placed in the manner of a closefit on the bush 12. Viewed in the radial direction, the collar 92 of thefilter 80 that encloses the end of the bush 12 is adapted to the bush 12in such a way that once the filter 80 and bush 12 have been puttogether, a press-fit is created between the bush 12 and the collar 92and accomplishes the retention of the filter 80 on the bush 12.

The ring 86a, oriented toward the bush 12, of the filter scaffold 84forms a loss-prevention means for the piston 20 before these parts areinstalled in the pump housing 16. The inside diameter of the ring 86a issmaller than an outside diameter of the end of the piston 20 locatedinside the bush 12. In the selected preferred exemplary embodiment, thesupport ring 58 belongs to the end of the piston 20 located inside thebush 12, and thus in this exemplary embodiment the inside diameter ofthe ring 86a of the filter 80 is smaller than the outside diameter ofthe support ring 58.

Via the support ring 58, the piston 20 has an encompassing shoulder 93,oriented toward the filter 80, on its face end. As long as the pistonpump 10 has not yet been inserted into the pump housing 16, the ring 86aretains the piston 20 on its support ring 58 in the bush 12. Before thebush 12 is installed in the pump housing 16, the piston 20 can protrudeout of the bush 12 only far enough that the shoulder 93 of the piston 20comes to rest on the filter 80.

The connection between the filter 80 and the bush 12 that results fromthe press fit between the collar 92 and the bush 12 is thus dimensionedas sufficiently forceful that the piston restoring spring 54 cannotforce the piston 20 out of the bush 12. As a result, the filter 80 holdsthe piston 20 in the bush 12 securely together before the bush 12 isinserted, together with the filter 80 and the piston 20, into the pumphousing 16. The collar 92 may grip the bush from the outside, as shown,or engage it from the inside (not shown).

The assembly of the piston pump 10 of the invention is done by firstplacing the valve closing spring 68 and the valve ball 70 of the outletvalve 64 in the closure element 62. Next, the bush 12 is press-fittedinto the closure element 62 or connected to it by crimping, and thespring 54 is placed in the bush 12. After that, the piston 20, with thesupport ring 58 slipped onto it and with the guide ring 26 and sealingring 28 as well as the inlet valve 38 mounted on it, is inserted intothe bush 12. By subsequent axially pressing on of the filter 80, thepiston 20 is retained in the bush 12 in a manner secure against loss,and the piston pump 10 is preassembled as a compact, easily manipulatedstructural group. In the proposed piston pump embodied according to theinvention, a preassembled structural group is created that includes thepiston 20, the inlet valve 38, the piston restoring spring 54, theoutlet valve 64, the closure element 62, and the filter 80. After thepreassembly, the complete preassembled structural group is inserted intothe cylinder bore 14 of the pump housing 16. A press fit between thebush 12 and the cylinder bore 14 effects sealing between the inlet andoutlet sides, or in other words the low- and high-pressure sides, of thepiston pump 10. A caulking 94 of the pump housing 16 on the closureelement 62 brings about a pressure-tight closure of the cylinder bore 14on the high-pressure side of the piston pump 10 and fixes the bush 12 inthe pump housing 16.

The ring 86b of the filter 80 has an inside diameter that is no largeror only slightly larger than the outside diameter of the part of thepiston 20 that protrudes through the ring 86b. Even before thepreassembled structural group is inserted into the pump housing 16, thisaccordingly provides guidance of the piston 20 via the filter 80. Beforethe preassembled structural group is inserted into the pump housing 16,the end of the piston 20 protruding into the bush 12 is guided by theguide ring 26, and the end of the piston 20 protruding out of the bush12 is guided by the ring 86b of the filter 80.

In a modification of this, it is also possible to embody the filter 80in such a way that the guidance of the piston 20 takes place not in theregion of the ring 86b but rather in the region of the ring 86a. In thatcase, the ring 86a has an inside diameter only slightly larger than theoutside diameter of the part of the piston 20 protruding through thering 86b. To enable the fluid to flow into the interstice 34, the insidediameter of the ring 86a is interrupted at a plurality of points.

Because the rings 86a, 86b of the filter 80 comprise plastic, theguidance of the piston 20 by the filter 80 can be achieved easily andwithout particular production effort and expense, and without the needto fear damage to the piston 20. After the insertion of the bush 12 intothe pump housing 16, the piston 20 is no longer guided via the filter 80but rather via the two guide rings 22 and 26, and thus the demands madeof the material of the filter 80 can easily be met without effort orexpense.

Even before the preassembled structural group is inserted into the pumphousing 16, the piston 20 is guided and aligned with the aid of thefilter 80, so that the preassembled structural group can advantageouslybe installed in the pump housing 16 very easily. Among other factors,this substantially facilitates the introduction of the piston 20 intothe guide and sealing rings 22, 24 that have been placed in the pumphousing 16 beforehand.

FIGS. 2-4 show examples of other possibilities for securing the filter80, which forms a loss-prevention means for the piston 20, to the bush12. In the exemplary embodiment of FIG. 2, the bush 12 is provided onits open end, on the inside thereof, with a rounded groove 95, which isengaged by an outward-protruding radial collar 96 of the filter 80. Thegroove 95 is made by caulking 97 or by crimping of the bush 12 once thefilter 80 has been mounted on the bush 12. For its introduction into thebush 12, the radial collar 96 has a chamfer 98. The radial collar 96rests on the bush 12 all the way around, so that no dirt can thus getpast the filter to reach the interstice 34.

In the exemplary embodiment of FIG. 3, an edge 100 of the bush 12 isdeformed radially inward by crimping and forms an undercut 102, which isengaged from behind by the radial collar 96 of the filter 80. Thecrimping creates a durable connection between the filter 80 and the bush12.

In the exemplary embodiment of FIG. 4, the filter 80 is mounted on thebush 12 with a detent connection. In the vicinity of the open face endof the bush 12, a groove 104 is provided on its inside circumference.The groove 104 is preferably rectangular in cross section. A rectangularradial collar 106 of the filter 80 rests in this groove 104. Forintroducing the filter 80 into the bush 12, the bush 12 is provided withan inner chamfer 108. Because of the rectangular cross section of thegroove 104 and the radial collar 106, the filter 80 is retained so wellon the bush 12 that the filter 80 is not separated from the bush eitherby the force of the piston restoring spring 54 or by any pull that mightbe exerted on the piston 20.

In a modification of this exemplary embodiment, the groove 104 may forinstance be located on the outer circumference of the bush 12 instead.In that case, the radial collar 108 of the filter 80 protrudes radiallyinward and can engage the groove 104 in this way.

In the embodiment of FIG. 4, the ring 86b of the filter 80, remote fromthe bush 12, forms the loss-prevention means for the piston 20. Thisring 86b has a smaller inside diameter than the bush 12. Aside from asmall guide gap, the outside diameter of the end of the piston 20protruding into the bush 12 is equivalent to the inside diameter of thebush 12. Accordingly, the inside diameter of the ring 86b of the filter80 is smaller than the outside diameter of the end of the piston 20protruding into the bush 12.

In the exemplary embodiment shown as a detail in FIG. 4, the piston 20is embodied in stepped fashion; the end of the piston 20 protruding intothe bush 12 has a larger outside diameter than the end of the piston 20protruding out of the bush 12. This creates a shoulder 93 at the piston20. Before the preassembled structural group is inserted into the pumphousing 16, the ring 86b of the filter 80 firmly retains the piston 20via the shoulder 93, so that the piston 20 cannot slide out of the bush12.

The filter 80 rests sealingly with its rings 86 on the bush 12 and onthe cylinder bore 14, in order to prevent liquid flowing to the pistonpump 10 from flowing into the piston pump 10 without passing through thefilter screen 82 and the filter cloth 90.

In the embodiments of FIGS. 2-4, the filter 80 can also grip the bush 12on the outside (not shown).

Via the shoulder 90, the filter 80 forming the loss-prevention meansretains the piston 20. As the preferred selected exemplary embodimentsshow, the shoulder 93 can be located integrally directly on the piston20 (FIG. 4), or else the shoulder 93 is located indirectly on the piston20 (FIG. 1), for instance via the support ring 58 connected to thepiston 20.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. A piston pump, comprising a pump housing, a bush in saidpump housing, a piston which is drivable to execute a reciprocatingstroke motion and is received axially displaceably at least partially insaid bush which is insertable into said pump housing, the piston pump(10) has a filter (80), which is mounted on the bush (12) and which hasa loss-prevention means (86a, 86b), that protrudes inward past an endedge of the bush (12), that keeps the piston (20) in the bush (12), andthe filter (80), in the region of the loss-prevention means has aninside diameter which is smaller than an outside diameter of the piston(20).
 2. The piston pump according to claim 1, in which the filter (80)is embodied hollow-cylindrically.
 3. A piston pump, comprising a pumphousing, a bush in said pump housing, a piston which is drivable toexecute a reciprocating stroke motion and is received axiallydisplaceably at least partially in said bush which is insertable intosaid pump housing, the piston pump (10) has a filter (80), which ismounted on the bush (12) and which has a loss-prevention means (86a,86b), that protrudes inward past an end edge of the bush (12), thatkeeps the piston 20 in the bush (12), and the filter (80) is mounted onthe bush (12) in an extension of the bush (12).
 4. The piston pumpaccording to claim 3, in which the filter (80) and the bush (12) arejoined together in the manner of a close-tolerance fit.
 5. The pistonpump according to claim 4, in which the filter (80), for being securedto the bush (12), has a press fit with regard to the bush (12).
 6. Thepiston pump according to claim 3, in which the filter (80) is mounted onthe bush (12) via a snap or detent connection (95, 96; 104, 106).
 7. Thepiston pump according to claim 3, in which the filter (80) is mounted onthe face end of the bush (12) by means of a local deformation.
 8. Apiston pump, comprising a pump housing, a bush in said pump housing, apiston which is drivable to execute a reciprocating stroke motion and isreceived axially displaceably at least partially in said bush which isinsertable into said pump housing, the piston pump (10) has a filter(80), which is mounted on the bush (12) and which has a loss-preventionmeans (86a, 86b), that protrudes inward past an end edge of the bush(12), that keeps the piston (20) in the bush (12), and theloss-prevention means forms guides (86a, 86b) on the filter (80) thatguides the piston (20).